The invention relates to a solar cell which facilitates conversion of energy from the sun at a high degree of efficiency and at low cost.
The main problem of the terrestrial use of solar cells lies, as is known, in the manufacture of a sufficiently cheap solar cell with the highest possible degree of efficiency. Since the cost of silicon plays a key role in this, there has been no lack of attempts to break away from expensive monocrystalline material and to use polycrystalline or amorphous silicon for solar cells. Unfortunately, solar cells made from these materials have poor efficiency.
The concept of the MIS and MISIM solar cells (M. A. Green and R. B. Godfrey) "The MIS and MISIM Solar Cell" Proceedings of the 1st International Photovoltaic Solar Energy Conference, Sept. 27-30, 1977, pp. 299-307) represents a substantial step forward in improving the degree of efficiency of polycrystalline solar cells. M stands for metal, I for a very thin insulator layer, and S for semiconductors. The grain limit recombination of polycrystalline material in these structures is largely eliminated. The concentration and increase in intensity of incident sunlight is a further measure for increasing the degree of efficiency of a solar cell. Since the temperature coefficient for maximum power in a silicon solar cell is, say 0.5% per degree, the efficiency when heating the solar cell from 0.degree. C. to 100.degree. C. is reduced approximately 50%. For this reason, the solar cell must be cooled reliably in the case of concentrated sunlight. This additional cooling and the means for concentrating the sunlight involve additional costs.